Electronic appliances have become smaller and more sophisticated and can be easily carried around. Thus, there is a demand for an environment in which a wireless communication device (a node) can be connected to a network when necessary and communication is enabled. As such an environment, a network temporarily created as necessary, that is, a wireless ad hoc network technology is being developed. In this wireless ad hoc network, without setting specific access points, individual wireless communication devices (for example, computers, portable information terminals (PDA: Personal Digital Assistance), portable telephones, and the like) which are autonomously distributed are connected by relaying frames to one another.
In this wireless ad hoc network, broadcast signals such as broadcast packets are sequentially sent via other wireless communication devices. Such sending of signals is called flooding (flooding). In the case of such flooding, when each node simply rebroadcasts broadcast packets that have not been previously received, if the number of nodes on a network increases, the number of broadcast packets on the network increases. As a result, a problem occurs in that flooding increases the network load.
Moreover, in general, broadcast packets are not retransmitted. Thus, when the number of broadcast packets increases within a network, packet loss due to collision increases in a case of CSMA/CA, which is a common wireless network access method. As a result, the reliability of flooding significantly decreases. Thus, for a wireless ad hoc network, there is a demand for an effective flooding method that prevents the number of broadcast packets from exponentially increasing when the number of nodes increases within the network.
At present, a technology called MPR (Multi Point Relay) is known as an effective flooding method for wireless ad hoc networks. This MPR technology is a method that is also employed as a flooding technology in OLSR (Optimized Link State Routing, RFC3626), which is a proactive routing protocol employed by the IETF (Internet Engineering Task Force) MANET WG (Mobile Ad-Hoc Network Working Group) (For example, see T. Clausen et al.: “Optimized Link State Routing Protocol (OLSR)”, RFC 3626, Network Working Group, IETF (http://www.ietf.org/rfc/rfc3626.txt).
MPR is a technology for “effectively” flooding all nodes existing on a network with broadcast packets. Here, “effectively” means that, without all nodes rebroadcasting broadcast packets, the number of nodes that are allowed to rebroadcast is limited in accordance with a network status, whereby the number of broadcast packets to be transmitted to a network is reduced. First, each node selects and sets a node called an “MPR node” from among neighbor nodes. Then, the node sends a notification of information regarding the MPR node to neighbor nodes. A node selected as an MPR node rebroadcasts broadcast packets that are transmitted from nodes that set the node as an MPR node. Thus, flooding can be executed without all nodes rebroadcasting broadcast packets. That is, in an MPR technology, how to select MPR nodes is important.
However, in an actual wireless ad hoc network, communication states of links between all neighbor nodes may not be two-way stable states on every occasion, and there may be an unstable-state link in which packet error often occurs. There is a high probability that a link in which packet error often occurs may be temporarily determined as a one-way link. Thus, in a case where flooding using MPR nodes is applied, flooding may not be performed for nodes whose link state is unstable. With consideration of wireless propagation paths, the probability is sufficiently high that packet errors occur in a burst manner, thus it is necessary to attempt flooding even for nodes having a link whose communication state is unstable; however, the present MPR technology is not entirely appropriate therefor.
Thus, an object of the present invention is to set optimal MPR nodes with consideration of communication states of links in a wireless ad hoc network.
The present invention has been made to solve the above-described problems. A first aspect of the present invention is a wireless communication device that performs communication, in a route via a neighbor wireless communication device, with another wireless communication device that exists outside a wireless communication range of the wireless communication device, characterized by including: unidentified-device identification-information holding means for holding, as unidentified-device identification information, information used to identify an unidentified device that is another wireless communication device to which the reachability of a signal whose transmission source is the wireless communication device has not been verified; relay-device identification-information holding means for holding information used to identify a relay device that is another wireless communication device that relays a signal whose transmission source is the wireless communication device; and relay-device setting means for treating, as first destination stations, other wireless communication devices that exist within a wireless communication range of the wireless communication device, treating, as second destination stations, other wireless communication devices that exist outside the wireless communication range of the wireless communication device and within wireless communication ranges of the first destination stations, selecting at least one of the first destination stations as the relay device in accordance with communication states between the wireless communication device and the first destination stations and communication states between the first destination stations and the second destination stations, holding information used to identify the selected relay device in the relay-device identification-information holding means, and deleting information used to identify a wireless communication device whose reachability has been verified via the selected relay device from the unidentified-device identification-information holding means, until the unidentified-device identification information held in the unidentified-device identification-information holding means becomes nonexistent. Thus, it becomes possible for a relay device to be selected in accordance with a communication state between wireless communication devices.
Moreover, in this first aspect, in a case where a specific second destination station having only one link to one of the first destination stations exists in the second destination stations whose unidentified-device identification information is held in the unidentified-device identification-information holding means, if both a communication state between the specific first destination station and the wireless communication device and a communication state between the specific first destination station and the specific second destination station are stable states, the relay-device setting means may select the specific first destination address as the relay device. Thus, in a case where there exists a specific second destination station having only one link to one of first destination stations, it becomes possible for a relay device to be selected in such a manner that relaying is preferentially performed to such a second destination station. Moreover, in this case, when at least either a communication state between the specific first destination station and the wireless communication device or a communication state between the specific first station and the specific second destination station is an unstable state, if there exists a first destination station which is other than the specific first destination station and whose communication state with the wireless communication device is a stable state, the relay-device setting means may select such a first destination station as the relay device, and if such a first destination station does not exist, the relay-device setting means may select the specific first destination station as the relay device. Thus, if a communication state of a route via a first destination station other than a specific first destination station is stable, it becomes possible for a relay device to be selected in such a manner that such a route is prioritized.
Moreover, in this first aspect, in a case where no specific second destination station having only one link to one of the first destination stations exists in the second destination stations whose unidentified-device identification information is held in the unidentified-device identification-information holding means, the relay-device setting means may select a first destination station that is more stable and that has a large number of links as the relay device, in accordance with communication states and the number of links between the second destination stations whose unidentified-device identification information is held in the unidentified-device identification-information holding means and the first destination stations and communication states between the first destination stations and the wireless communication device. Thus, in a case where there exists no second destination station having only one link to one of first destination stations, it becomes possible for a relay device that can perform stable relaying to more number of second destination stations, to be selected.
Moreover, a second aspect of the present invention is a wireless communication device that performs communication, in a route via a neighbor wireless communication device, with another wireless communication device that exists outside a wireless communication range of the wireless communication device, characterized by including: unidentified-device identification-information holding means for holding, as unidentified-device identification information, information used to identify an unidentified device that is another wireless communication device that exists within a wireless communication range to which the reachability of a signal whose transmission source is the wireless communication device has not been verified; relay-device identification-information holding means for holding information used to identify a relay device that is another wireless communication device that relays a signal whose transmission source is the wireless communication device; and relay-device setting means for selecting the relay device in accordance with a communication state between the wireless communication device and the other wireless communication device, holding information used to identify the selected relay device in the relay-device identification-information holding means, and deleting information used to identify a wireless communication device whose reachability has been verified via the selected relay device from the unidentified-device identification-information holding means, until the unidentified-device identification information held in the unidentified-device identification-information holding means becomes nonexistent. Thus, it becomes possible for a relay device to be selected in accordance with a communication state with another wireless communication device that exists within a wireless communication range.
Moreover, in this second aspect, in a case where there exists the other wireless communication device whose communication state with the unidentified device whose unidentified-device identification information is held in the unidentified-device identification-information holding means is a stable state, the relay-device setting means may select the other wireless communication device as the relay device. Thus, if a communication state between an unidentified device that exists within a wireless communication range and another wireless communication device that exists within the wireless communication range is a stable state, it becomes possible for such another wireless communication device to be selected as a relay device.
Moreover, a third aspect of the present invention is a wireless communication system in which wireless communication devices each perform communication, in a route via a neighbor wireless communication device, with another wireless communication device that exists outside a wireless communication range of the wireless communication device, characterized by including: each of the wireless communication devices including unidentified-device identification-information holding means for holding, as unidentified-device identification information, information used to identify an unidentified device that is another wireless communication device to which the reachability of a signal whose transmission source is the wireless communication device has not been verified; relay-device identification-information holding means for holding information used to identify a relay device that is another wireless communication device that relays a signal whose transmission source is the wireless communication device; and relay-device setting means for treating, as first destination stations, other wireless communication devices that exist within a wireless communication range of the wireless communication device, treating, as second destination stations, other wireless communication devices that exist outside the wireless communication range of the wireless communication device and within wireless communication ranges of the first destination stations, selecting at least one of the first destination stations as the relay device in accordance with communication states between the wireless communication device and the first destination stations and communication states between the first destination stations and the second destination stations, holding information used to identify the selected relay device in the relay-device identification-information holding means, and deleting information used to identify a wireless communication device whose reachability has been verified via the selected relay device from the unidentified-device identification-information holding means, until the unidentified-device identification information held in the unidentified-device identification-information holding means becomes nonexistent. Thus, it becomes possible for a relay device to be selected in accordance with a communication state between wireless communication devices in a wireless communication system.
Moreover, a fourth aspect of the present invention is a wireless communication system in which wireless communication devices each perform communication, in a route via a neighbor wireless communication device, with another wireless communication device that exists outside a wireless communication range of the wireless communication device, characterized by including: each of the wireless communication devices including unidentified-device identification-information holding means for holding, as unidentified-device identification information, information used to identify an unidentified device that is another wireless communication device that exists within a wireless communication range to which the reachability of a signal whose transmission source is the wireless communication device has not been verified; relay-device identification-information holding means for holding information used to identify a relay device that is another wireless communication device that relays a signal whose transmission source is the wireless communication device; and relay-device setting means for selecting the relay device in accordance with a communication state between the wireless communication device and the other wireless communication device, holding information used to identify the selected relay device in the relay-device identification-information holding means, and deleting information used to identify a wireless communication device whose reachability has been verified via the selected relay device from the unidentified-device identification-information holding means, until the unidentified-device identification information held in the unidentified-device identification-information holding means becomes nonexistent. Thus, it becomes possible for a relay device to be selected in accordance with a communication state with another wireless communication device that exists within a wireless communication range.
Moreover, a fifth aspect of the present invention is a wireless communication method in a wireless communication device that is one of wireless communication devices each performing communication, in a route via a neighbor wireless communication device, with another wireless communication device that exists outside a wireless communication range of the wireless communication device and including unidentified-device identification-information holding means for holding, as unidentified-device identification information, information used to identify an unidentified device that is another wireless communication device to which the reachability of a signal whose transmission source is the wireless communication device has not been verified and relay-device identification-information holding means for holding information used to identify a relay device that is another wireless communication device that relays a signal whose transmission source is the wireless communication device, characterized by including: a selection process of treating, as first destination stations, other wireless communication devices that exist within a wireless communication range of the wireless communication device, treating, as second destination stations, other wireless communication devices that exist outside the wireless communication range of the wireless communication device and within wireless communication ranges of the first destination stations, selecting at least one of the first destination stations as the relay device in accordance with communication states between the wireless communication device and the first destination stations and communication states between the first destination stations and the second destination stations, and holding information used to identify the selected relay device in the relay-device identification-information holding means; and a deletion process of deleting information used to identify a wireless communication device whose reachability has been verified via the selected relay device from the unidentified-device identification-information holding means, wherein the selection process and the deletion process are repeated until the unidentified-device identification information held in the unidentified-device identification-information holding means becomes nonexistent, or a program characterized by causing a computer to repeatedly execute these processes until the unidentified-device identification information held in the unidentified-device identification-information holding means becomes nonexistent. Thus, it becomes possible for a relay device to be selected in accordance with a communication state between wireless communication devices.
Moreover, a sixth aspect of the present invention is a wireless communication method in a wireless communication device that is one of wireless communication devices each performing communication, in a route via a neighbor wireless communication device, with another wireless communication device that exists outside a wireless communication range of the wireless communication device and including unidentified-device identification-information holding means for holding, as unidentified-device identification information, information used to identify an unidentified device that is another wireless communication device to which the reachability of a signal whose transmission source is the wireless communication device has not been verified and relay-device identification-information holding means for holding information used to identify a relay device that is another wireless communication device that relays a signal whose transmission source is the wireless communication device, characterized by including: a selection process of selecting the relay device in accordance with a communication state between the wireless communication device and the other wireless communication device and holding information used to identify the selected relay device in the relay-device identification-information holding means; and a deletion process of deleting information used to identify a wireless communication device whose reachability has been verified via the selected relay device from the unidentified-device identification-information holding means, wherein the selection process and the deletion process are repeated until the unidentified-device identification information held in the unidentified-device identification-information holding means becomes nonexistent, or a program characterized by causing a computer to repeatedly execute these processes until the unidentified-device identification information held in the unidentified-device identification-information holding means becomes nonexistent. Thus, it becomes possible for a relay device to be selected in accordance with a communication state with another wireless communication device that exists within a wireless communication range.
According to the present invention, a superior effect of being capable of setting optimal MPR nodes with consideration of communication states of links can be obtained in a wireless ad hoc network.